1. Field of the Invention
Present invention is related generally to a defect inspection apparatus for patterns which are used to detect the defects on patterns of the inspected subject.
2. Description of the Prior Art
Upon manufacturing semi-conductors or printed circuit boards, it is common that a photomask which contains a certain pattern is used. In such case, if there is a defect on the pattern of the photomask it will cause reject products and accordingly inspection for defects on the pattern of the photomask is an important process. A pattern defect inspection apparatus example based upon the prior art will be explained hereunder in reference with FIGS. 1, 2 and 3.
FIGS. 1 and 2 show a portion of a photomask as magnified by a microscope and on such drawings, 1 and 1' are photomasks of transparent material such as glass or the like, 2 and 2' show in general a pattern which is formed with, for example, evaporated metal or the like on photomasks 1 and 1', 3 is the transparent portion of the transparent base plate of photomasks 1 and 1', and 4 is the nontransparent or opaque portion by the evaporated material respectively. On FIG. 2, A and B are flaws formed by excess evaporated material unnecessarily remaining, and C and D are the portions where the necessary evaporated material is lacking. Accordingly, the photomask 1' which has the pattern 2' as shown on FIG. 2, is a defective product. On the other hand, the photomask 1 as shown on FIG. 1 is a complete normal product.
In order to inspect photomask 1 or 1' as shown on FIGS. 1 and 2 under the prior art, for instance, as shown on FIG. 3, a standard mask 6 which has a complete pattern (for instance as shown as pattern 2 on FIG. 1) is placed at a specified location on a transparent base 5. A mask 7 which is to be inspected (for instance, the defective mask such as shown on FIG. 2) is placed at another specified location on the base 5. Both masks are observed by a binocular microscope 8. On FIG. 3, 9 and 10 are the objective lenses for standard mask 6 as well as the inspected mask 7, 11 and 12 are the mirrors for both masks 6 and 7, in the same respect, 13 and 14 are the half mirrors for the masks 6 and 7, 15 is a common eye piece lens, 16 is the light source such as a red light which irradiates on standard mask 6 and 17 is another light source that irradiates a green light for instance which is the complimentary colour to red, which is irradiated on the inspected mask 7. Therefore, the lights that are irradiated from light sources 16 and 17 pass through the base 5, masks 6 and 7, lenses 9 and 10, mirrors 11 and 12, half mirrors 13 and 14, and further pass through lens 15 of the binocular microscope 8 to form an image at an observing eye 18, which makes the inspection of mask possible. When the inspected mask 7 is a defective product such as shown on FIG. 2, at portions A and B, the green light that is irradiated from light source 17 is shielded by portions A and B so that only the red light which is irradiated from light source 16 arrives at the observing eye 18, and hence these portions A and B appear red in colour. On the other hand, at portions C and D, the red light from light source 16 is shielded, and only the green light from light source 17 arrives at the observing eye 18, so that such portions C and D appear green in colour. For the other portions, which are the transparent section 3, the red and green lights as irradiated from light sources 16 and 17 respectively arrive at the observing eye 18 simultaneously and accordingly appear generally as white, and as for the nontransparent section 4, both of the red and green lights are shielded and do not pass which appears to be generally in black. In other words, when the entire view appears in white or black, there is no defect on the inspected mask 7, while when even a slight shade of red or green colour appears, the inspected mask 7 contains a defect.
The above described pattern inspection apparatus under the prior art has the fault that the inspected subject must be transparent and further since each piece must be inspected by human eyes, in order to automate this inspection process, an expensive colour television camera becomes necessary.